P0B39: Motor Electronics Coolant Pump B Control Circuit Low
What to do
As P0B38 — and if you can hear a pump still running well after the car has been switched off and locked, say so. That points here specifically, and left alone it will both wear out the pump and flatten the 12-volt battery.
What this code means
The control circuit for the second electronics coolant pump is reading low — a short to earth, or a driver output that has failed closed.
One consequence is specific to the low direction and worth naming: a control output shorted to earth can leave the pump running continuously, which cools perfectly well but wears the pump out and, on some designs, prevents the vehicle from powering down properly. A pump you can still hear running some time after the car is locked belongs to this code rather than to the open one.
The second-loop argument, and the slow-charging symptom, are at P0B38.
Likely causes
Start here
- Wiring shorted to ground · moderate
- Faulty inverter coolant pump · moderate
Less common
- Corroded or loose connector · easy
- Damaged wiring harness · moderate
Symptoms
Components involved
Information, not instruction
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Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
Community experience
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